package com.company.jd;

import java.util.Scanner;

public class Main2 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double res = getSum(n);
        System.out.printf("%.4f",res);
    }

    private static double getSum(int n) {
//        if(n == 1){
//            return 0.1000;
//        }
        int[] list = new int[n + 1];
        for(int i = 1;i <= n;i++){
            int temp = (2 * i - 1 ) * 2 * i;
            list[i] = temp;
        }
        // 最小公倍数
        int nth_leastMcd = list[1];
        for(int i = 2;i <= n;i++){
            nth_leastMcd = mcd(nth_leastMcd,list[i]);
        }
        int sum_Fenzi = 0;
        for(int i = 1;i <= n;i++){
            sum_Fenzi += nth_leastMcd / list[i];
        }

        double res = sum_Fenzi / (5.0  * nth_leastMcd);
        return res;

    }

    private static int mcd(int a,int b){
        return a * b / gcd(a,b);
    }

    private static int gcd(int a,int b){
        if(a > b){
            int temp = b;
            b = a;
            a= temp;
        }
        while (b != 0){
            int temp = a ;
            a = b;
            b = temp % b;
        }
        return a;
    }
}
